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Managers - Confused!

 
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Super Advisor

Managers - Confused!

I have a single Management Group with two sites.

I have two multi-site clusters.

Cluster1 has 2 SAS nodes.

Cluster2 has 4 MDL nodes.

The nodes are assigned to the sites and there is an equal number in each site.

Right now I'm running 2 managers on nodes 1/2 in Cluster1 which is because when we configured the initial management group we added 2 nodes to create Cluster1 and the wizard setup the nodes.

The Best Practise Wizard is suggesting that now I have 6 nodes total I should have 4 managers and a FOM (the FOM will be added on the local storage of our primary site's vSphere server later).

What the Best Practise Wizard isn't telling me, is which of the 4 new (or 6 total) nodes I should be running the 4 managers on, and I'm struggling to make it out from the documentation.

Which should I be running them on and why please?

Thanks,
Paul
19 REPLIES 19
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Solution

Re: Managers - Confused!

Yep, I had the same confusion on this as well. All said and done, you need 1 FOM per management group and then all nodes run a standard manager. I think you have to delete the Virtual Manager before it will let you add the FOM.
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Super Advisor

Re: Managers - Confused!

Thanks Jim.

Where the documentation falls down is making that clear I think.

Should I really be running 6 managers though? I ask as the CMC best practise analyser suggests 4 (+ FOM) yet the documentation suggests (p148-149 of c02008676.pdf) that if you create a management group with "3 or more" nodes it will only configure 3 managers - I thought the whole point of managers was you need an even number in each site + a virtual manager or FOM to cast the deciding vote?

Also is manager status retained after a node restarts?
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Respected Contributor

Re: Managers - Confused!

I always understood it to be that you have to have an odd number of total managers, with a maximum of 5.

Not sure why there is the max of 5, unless perhaps it gets to be too much metadata to efficiently replicate beyond 5 managers...

The problem I always ran into, was that you could not obtain node level SNMP performance metrics unless that node was running a manager, although I haven't seen if this issue is different in SAN/iQ 9.0
http://www.tdonline.com
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Super Advisor

Re: Managers - Confused!

I think where I've been getting confused is that whilst testing I only had 2 nodes so quorum/managers was easy - 2 physical + FOM/Virtual.

Now I have six nodes and (minimum) of two clusters I think I made the mistake of thinking that managers/quorum applied to the *clusters* rather than to the *management group*.

So as per c02063195.pdf, on page 11 Figure 3, I'd use 4 managers, 2 per site.

In theory the managers can be random nodes, but as I currently have 2 clusters, I'd make one node per cluster per site (1 node x 2 clusters x 2 sites = 4 managers) + FOM.

Does that sound about right on the misunderstanding and the solution?
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Honored Contributor

Re: Managers - Confused!

Hi,
In a management group it does not matter how many clusters you have as long as you have the correct amount of manager processes running to maintain quorum, because this is for the whole management group.
In your situation with 6 physical nodes you could run with 5 node managers and have NO FOM and that would be fine. If one manager node were to fail then you could still turn on the manager on the node that was not running a manager to take you back up to 5.
I have always been told to only have a max of 5 managers in a management group as well. I believe it is to do with the management overhead as well as a previous person has mentioned.
Therefore in your current situation you could run:
5 managers
4 managers + FOM
4 managers + VM
Again it has been mentioned that you are not able to have a FOM and a VM in a management group.
As you have also said, it would make sense to split your managers across both sites and then to decided which site would be your primary site to have the 5th manager/FOM. HP do recommend that FOM should be on site "C" for resiliance.
Remember you only start VM when you lose quorum so this would give you the flexibility to decide which site you would like to remain running but it is a manual process.
Mark...
if you have nothing useful to say, say nothing...
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Super Advisor

Re: Managers - Confused!

Yeah I've realised that's my schoolboy error :)

So in my situation seems to call for Site A designated "Primary" in the CMC with:

Site A, Cluster 1 - 1 manager
Site A, Cluster 2 - 1 manager
Site A, FOM (on local VMFS)

Site B, Cluster 1 - 1 manager
Site B, Cluster 2 - 1 manager

What would happen to if I lost the FOM though, or just needed to restart the system it's running on?
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Honored Contributor

Re: Managers - Confused!

Hi,
Loss of FOM or a node of two would still not be a problem as long as you maintain Q.
Example- 4 man + fom = 5 = Q of 3
Loss of FOM = 4, Q still = 3 - stays up just restart FOM when able.
Loss of node = 4, Q still =3 - so stays up again.
In both cases, being as you have at least 2 nodes not running manager process then there is nothing to stop you starting manager on one of those nodes to maintain your 5 votes.
Once you have fixed the problem then you can just stop / start managers as required
Hope that helps.
Mark...
if you have nothing useful to say, say nothing...
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Super Advisor

Re: Managers - Confused!

Thanks Mark, I think I'm there now - like the flexibility of the P4000, not so keen on all the "what if's" it raises :)

Toying with one of those cheap HP Microserver's to run the FOM on rather than have it on the main vSphere host in that location as it could also double up as a router/firewall between the iSCSI VLAN and the production LAN.
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Honored Contributor

Re: Managers - Confused!

Hi Paul,
Any PC running XP will do as you can create a FOM on there if you wish. You just need to run it under the ESX player or whatever it is!
Regards,
Mark...
if you have nothing useful to say, say nothing...